1. Field of the Invention
The present invention relates to an image processing method and an apparatus for performing color processing by using interpolation processing, and a recording medium.
2. Description of the Related Art
Hitherto, representative of this type of apparatus, a color correction processing apparatus is known, such as a color ink jet printer, for performing recording by causing ink to be deposited onto a surface. In such apparatuses, for example, it is necessary to provide an input signal in the form of luminance signals of R (red), G (green) and B (blue) which are dependent upon a device, and to obtain density signals corresponding to each of the colors C (cyan), M (magenta), Y (yellow) and K (black) as output signals. Also, by taking the portability of image data into consideration, in such a processing system a method has recently been proposed in which an input signal is once converted into a color space, which is not device dependent, such as the CIE 1931 XYZ color space or the CIE1976LAB color space, determined by the Commission Internationaldel Eclairage (abbreviated as CIE), and converted into a density signal dependent upon an output device. At this time, the color correction processing apparatus must perform many processes (the details of which are omitted here), as shown in FIG. 2.
Accordingly, a method is proposed in, for example, Laid-Open Japanese Patent Nos. 7-193723 and 8-237497, in which the results, such that this series of processing is performed in advance on a specific input signal, are stored in a N-dimensional look-up table (LUT), and an interpolation computation is performed by referring to the LUT, thereby obtaining an output signal corresponding to a desired input signal.
Since all of these methods take an orthogonal coordinate system of RGB and the like as an input signal and obtain an output signal by linear interpolation, there is the drawback of the interpolation accuracy being poor.
Meanwhile, in Laid-Open Japanese Patent No. 5-46750, a method is proposed in which an RGB input signal is converted into hue, chromaticity and brightness, and this is interpolation-computed by referring to a two-dimensional or three-dimensional LUT, thereby obtaining an output signal corresponding to a desired input signal. In these methods, the object is to increase the accuracy by converting an input signal into a signal appropriate for a visual characteristic. However, in the former case conversion into a polar coordinate system must be performed, and in the latter case conversion into a YCrCb coordinate system must be performed, giving rise to the drawback of the processing becoming heavily loaded.
Also, in Japanese Patent Publication No. 7-119128, as a method for converting an RGB input signal into hue, chromaticity and brightness, a method simplified by comparing the relationship of the RGB input signals is proposed. However, in these proposals, since many processes, such as those shown in FIG. 2, are not considered, there is the drawback that an interpolation computation using a LUT cannot be performed.
As described above, each of the conventional technologies has drawbacks such as the interpolation accuracy being poor, and the processing becoming heavily loaded.